Injectable fastener system and method

Abstract

Methods and devices are shown for forming polymer fasteners into bone by expelling the polymer from a cannula. devices and methods shown allow a user to form multiple fasteners of various sizes without re-loading a device. devices and methods shown further provide temperature profiles during fastener formation that reduce or eliminate thermal necrosis. devices and methods shown further provide fasteners with increased strength.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 121 that are powered by the battery or batteries 106. Materials that these electrically resistive elements 121 can be manufactured from include, but are not limited to, nickel chromium wire, conductive plastics, ceramics, quartz, etc. In alternative embodiments, the methods of producing heat may include, but are not limited to, induction, radio frequency, vibrational, ultrasonic, microwave, frictional, exothermic chemical reactions and infrared. The temperature can either be controlled actively or passively. Any known method of active temperature control could be utilized including sensing the temperature through a temperature sensor and utilizing this to control the amount of power going to the heater 123 (shown schematically). Resistive heating elements 121 that have a resistance that increases with increasing temperature (positive temperature coefficient or PTC) can provide a means of self regulating their temperature actively without additional controls. In alternate embodiments the temperature is controlled passively without active regulation.

In one embodiment, the polymer includes a thermoplastic polymer 122. On example of a thermoplastic polymer includes a bioresorbable aliphatic polyester. Aliphatic polyesters that can be used in this device include, but are not limited to, homo- and co-polymers of polylactic acid, polyglycolic acid and polycaprolactone. These polymers have been used for a number of years in orthopedic devices and are generally regarded as biocompatible and bioresorbable. In the preferred embodiment the polymer is substantially non-crystalline, but at least partially crystalline polymers could be used. Other biocompatible but non-resorbable polymers could be used in instances where the resorbability was undesirable. Non-resorbable polymers that could be used include, but are not limited to, acrylic, polycarbonate, PEEK, polypropylene, and polyethylene.

In one embodiment, the thermoplastic polymer 122 is compounded with an agent to increase radiopacity, osteoconductivity, osteoinductivity or deliver a therapeutic agent. Possible radiopacifiers include, but are not limited to, barium sulfate, zirconium oxide, titanium oxide, titanium dioxide, calcium, tantillum and iodine. Agents to increase osteoconductivity include, but are not limited to, hydroxyapatite, calcium phosphate and calcium sulfate. Agents to increase osteoinductivity include, but are not limited to, bone morphogenic proteins and growth factors. Therapeutic agents include, but are limited to, antibiotics, antiseptics, analgesics, chemotherapeutics, and pain medications.

As mentioned above, in one embodiment the chamber 120 and polymer 122 are coordinated together as a replaceable cartridge. This configuration provides a disposable delivery vessel for the polymer to obviate the need to clean the internal mechanisms and chambers of the injection device. One example chamber 120 in a cartridge embodiment is constructed of a heat resistance metal such as stainless steel or aluminum or of a heat resistant, biocompatible polymer such as PEEK, polysulphone, Radel, or polycarbonate.

In selected polymer cartridge embodiments, the cartridge further includes a cartridge plunger 126 that expels the polymer when advanced. In one embodiment the cartridge plunger 126 is integral to the polymer cartridge and is disposed of along with the polymer cartridge. In alternative embodiments, the cartridge plunger 126 is a part of the bone support attachment device 100 and separated by a seal from the polymer 122. The advancement of the cartridge plunger 126 is controlled by the bone support attachment device 100 as described in more detail below.

In an alternate embodiment the polymer 122 is provided in discrete sections that are not heated in the chamber 120. The volume of each section would correspond to the desired volume of each fastener. In this embodiment the unheated sections are individually transferred to the injection cannula through a mechanism, or manually. They are then individually heated in the injection cannula 140. In one embodiment, they are stacked in a linear or circular array. Alternately, they could be transferred individually into the injection cannula by the user without the aid of an internal mechanism or cartridge.

In one embodiment, one or more heating elements 141 are provided at a tip region 150 surrounding the injection cannula 140. The heating elements 141 in the tip region provide further control of the polymer temperature as it comes into contact with tissue and forms a fastener.

In one embodiment the injection cannula 140 is actively heated in the entire region from the first end 142 to the second end 144. In one embodiment at least part of the heat for the injection cannula is generated through an actively regulated heater 143 (shown schematically) in order to maintain consistent temperatures. Once the cannula exits the distal tip, it is exposed to variable thermal conditions (i.e. dry bone, wet bone, room temperature, physiological temperature). Active temperature regulation will help to maintain a consistent temperature profile in the cannula. In one embodiment, a thermal gradient is provided in the injection cannula 140 where the polymer 122 is at a higher temperature in a proximal region 154 of the tip than at a distal end 152 of the tip 150. The higher temperature at the proximal end 154 facilitates improved flow characteristics, while the lower and more tightly controlled temperature at the distal end 152 reduces the possibility of necrosis in tissue. In one embodiment, multiple heating elements 141 and/or thermal control circuits are used to control the temperature gradient.

FIG. 2 shows a close of view of the tip 150 of the bone support attachment device 100 during formation of a fastener. A cross section view of a bone support structure 210 is shown located adjacent to a portion of bone 212. A hole 218 is included through the bone support structure 210 and a corresponding hole 220 is included in the bone 212.

In one embodiment, the bone support structure 210 includes a plate, although other forms of support structures are within the scope of the invention. In one embodiment, the bone support structure 210 is formed from a bioresorbable material such as a bioresorbable polymer. In one example, the bone 212 is a thin layer of bone, such as a portion of a skull, although the invention is not so limited. An interface 214 is formed between the bone support structure 210 and the bone 212. As shown in the Figure, frequently a gap is included at the interface 214.

In one embodiment, a depth gauge 112 is included near the tip 150 of the bone support attachment device 100. An example of a depth gauge includes a static shelf that butts against the bone support structure 210 and limits a depth that the injection cannula 140 travels within the holes 218 and 220. The depth gauge 112 determines where in the holes 218 and 220 the second end 144 of the injection cannula 140 is located. In one embodiment, the desired depth of the second end 144 is through the hole 218 in the bone support structure 210, past the interface 214 and partially into the hole 220 in the bone. By passing the interface with the second end 144, a possibility of polymer being extruded into a gap at the interface 214 is reduced or eliminated.

Extrusion of polymer between any gap at the interface is undesirable for a number of reasons. Any polymer that is accidentally extruded at the interface is not available to form structural portions of the fastener, therefore strength of the fastener is lessened by extrusion into a gap at the interface. Further, any extrusion at the interface tends to open any existing gap further.

In one embodiment, the depth gauge 112 is dynamic. For example, in one embodiment, once a predetermined volume of polymer is extruded into the holes 218, 220, the depth gauge is moved to retract the second end 144 of the injection cannula 140 from the holes 218, 220.

In selected embodiments, the position of the depth gauge 112 is user selectable to adapt to plates of various thicknesses and holes of different depths. In one embodiment the depth gauge 112 is larger than the hole 218 or any countersunk area around the hole 218 in the bone support structure 210. This allows the surgeon to compress the bone support structure 210 against the tip 150 against the bone 212. In an alternate embodiment the depth gauge 112 is slideably attached, and the second end 144 of the cannula 140 protrudes only when the instrument is compressed against the bone support structure 210. This feature would protect the second end 144 except when injection is about to take place. In one embodiment the second end 144 of the cannula 140 seals against a portion of the tip 150 so as to not allow extraneous fluid and matter to enter the inside of the injection cannula 140 or between the cannula and tip 150.

In one embodiment, the outer diameter of the second end 144 of the cannula 140 is slightly smaller than the hole 220 in the bone 212. Without implying limitation, this diameter would generally fall within the range of 1.3 to 3.5 mm at the most distal point. This is to allow the cannula 140 to enter the hole 220 in the bone 212 with minor resistance. In one embodiment, the hole 220 in the bone 212 is tapered or stepped to allow for a larger opening for entry of the cannula 140 and a smaller hole to minimize the amount of material required to fill the entire opening.

FIG. 2 further shows a volume of expelled polymer 160. The process of expelling a polymer in contrast to heating in place has an advantage of forming a cooled profile across the volume of expelled polymer 160. A surface 162 of the expelled polymer cools first on contact with tissue or other external surfaces. The interior of the expelled polymer remains flowable, and tends to form a desirable shape similar to blowing up a balloon. The balloon shape helps to form a mechanical bond in the bone 212 similar to a rivet. Additionally, the cooled surface 162 is far less likely to cause thermal necrosis with tissue it comes into contact with. In contrast, for example, polymer that is heated through sonic vibration in a hole in bone is hottest at the interface between the bone and the polymer.

In one embodiment, the plunger 130 has a slight clearance fit relative to the inner walls of the injection cannula 140. The clearance is generally within the range of 2 to 200 μm. The clearance should be small enough as to not allow polymer to flow past the distal tip of the plunger yet large enough as to not create mechanical interference. In one embodiment the plunger 130 rotates as it translates to create additional friction as it travel within the cannula 140. This friction produces heat which reduces the viscosity of any polymer which flows between the cannula 140 and plunger 130. This rotation can be achieved through the attachment of the plunger 130 to the rotating lead screw 108. In one embodiment the clearance is eliminated at the second end 144 of the cannula 140 and an interference fit is achieved. An interference fit helps to sever any polymer from the plunger 130 and cannula 140 at the end of the cycle.

In one embodiment, the entire plunger 130 or at least the distal end of the plunger 130 is manufactured from or coated with a non stick material such as silicone or PTFE. This prevents polymer from adhering to the plunger 130 after a formed fastener is completed.

As discussed above, in one embodiment, the temperature profile of injection cannula 140 is controlled to allow the polymer to remain sufficiently flowable yet not induce thermal necrosis into the bone at the second end 144. Thermal necrosis in living tissue is a complex time and temperature dependent relationship, but is often considered to begin when the tissue reaches 48° C. Additionally, the bone support device 210 or plate may begin to deform under thermal stress. If, for example, a polylactide/polyglycolide polymer is used, a suitable range around a glass transition temperature of 48-55° C. is used for the injection cannula 140.

The rate at which the polymer cools within the cannula is dependent upon the rate at which it travels. Thus a lower temperature of the cannula at the distal end could be permitted if the polymer travels at a high enough rate such that it does not have sufficient time to equilibrate with the temperature of cannula itself.

In one embodiment the tip 150 of the bone support attachment device 100 acts as a heat sink and dissipates the heat from distal portion of the cannula 140 allowing for reduced temperature. This dissipating effect can be optimized through the use of thermally conductive materials and designs to accentuate heat transfer through conduction and convection. Such materials include, but are not limited to, aluminum, aluminum filled polymers, copper, brass, conductive metal, silver, and thermally conductive polymers or ceramics. Designs to promote heat transfer include, but are not limited to fins, vanes, ribs, pins, and spikes, etc. Active cooling could also be incorporated including, but not limited to, syringe irrigation, gases (N₂, air or CO₂), liquid nitrogen, peltier effect devices, vortex chillers, pumped saline, fans and recirculating chilled liquids. These methods of cooling the second end 144 of the cannula 140 can also be used to cool the polymer head once it has been formed as disclosed below.

As the polymer exits the second end 144 of the cannula 140 and into the bone 212, it begins to flow and interdigitate into any pores within the bone 212. FIG. 3 illustrates the flow anticipated when a hole 308 is in relatively non porous material and the hole extends through the bone 304. In this case, the polymer expands on the far cortex and forms a bulbous tip 312 with a diameter larger than the hole created 308. This provides for a rivet-like effect with additional pullout resistance.

FIG. 3 further illustrates a strengthening property that is unique to an extrusion process as described in the present disclosure. During extrusion, through a plate 300 and into bone 320, polymer molecules 320 are stretched and aligned along a long axis of the fastener 310. The alignment of the polymer molecules provides significant increases in fastener strength. In selected embodiments, strength of the fastener is increased by up to at least 75% over non-extruded polymer. A number of process variables such as the temperature at or around the glass transition temperature during extrusion contribute to alignment of polymer molecules.

FIG. 4 illustrates the flow anticipated when a fastener 410 is injected into porous or cancellous bone 404. In this case the polymer can flow into the interstices 412 of the bone 404 and interdigitate with it. This also provides pullout resistance. The embodiment shown in FIG. 4 also illustrates alignment of molecules 420 and strengthening of the fastener 410.

Referring again to FIG. 3, the head 314 that is formed by the fastener is allowed to substantially fill a countersink recess 302 in the plate 300. This provides locking of the fastener 310 to the plate 300 yet allows rotational motion. If locking in rotation is also desired, the countersunk recess can be incorporate grooves or other surface irregularities that the polymer can flow into. The injected polymer and fixation device can also be bonded together if melted.

FIG. 5 illustrates an example of a bone plate 500. As discussed above, bone plates 500 are included in the category of bone support structure, however additional bone support structures other than plates are included within the scope of the invention. Holes 504 are shown to accept polymer fasteners as described in embodiments above. Other plate portions 502 form structure between the holes 504.

FIG. 6 illustrates one example use of bone plates in conjunction with polymer fasteners as described in embodiments above. A skull 600 is used as an example portion of bone. A first plate 604 is shown secured to the skull 600 using a number of bone plates 602 and polymer fasteners as described in selected embodiments above.

FIG. 7 illustrates an example method according to an embodiment of the invention. An amount of polymer is heated heating to a temperature at or above its glass transition temperature. A hole is drilled in a bone to accept a fastener. The hole in the bone is aligned with a hole in a support structure, such as a bone plate. A cannula is inserted through the hole in the support structure, past an interface between the support structure and the bone, and at least partially into the hole in the bone. As discussed above, the insertion of the cannula to this location helps prevent extrusion of polymer at the interface. Insertion of the cannula further aids in alignment of the holes. The heated amount of polymer is then expelled from a tip of a cannula, into the hole in the bone, and the cannula is removed from the hole in the bone and the hole in the support structure. The polymer left in the holes forms a fastener, as described in selected embodiments above.

While a number of example embodiments and advantages of the invention are described, the above examples are not exhaustive, and are for illustration only. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement or method which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments, and other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention includes any other applications in which the above structures and methods are used. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

The Abstract is provided to comply with 37 C.F.R. § 1.72 (b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. A bone support attachment device, comprising:

an injection cannula sized to hold an amount of polymer to form a single fastener;

a polymer supply inlet coupled to a side of the injection cannula;

a plunger having a tip disposed at a first end of the injection cannula such that, when actuated, the plunger expels the amount of polymer from a second end of the injection cannula upon the plunger reaching the second end of the injection cannula; and

a chamber sized to house a block of polymer sufficient to form a plurality of fasteners, the chamber having a first end having a chamber polymer supply inlet and a second end distal the first end and connected to the polymer supply inlet to sequentially provide the amount of polymer to form a single fastener from the chamber,; and,

the chamber including an actively regulated a chamber heater, adjacent the chamber and configured to actively regulate the chamber so as to maintain a temperature profile from a first end of the chamber to the second end of the chamber, wherein the temperature profile comprises a temperature gradient from the first end of the chamber to the second end of the chamber and wherein the temperature gradient is warmer at the second end of the chamber than at the first end of the chamber.

2. The bone support attachment device of claim 1, wherein the actively regulated chamber heater comprises multiple heating elements.

3. The bone support attachment device of claim 1, wherein the actively regulated chamber heater comprises multiple thermal control circuits.

4. A bone support attachment device of claim 1, further comprising an actively regulated a cannula heater disposed at a tip region of the device configured to actively regulate the injection cannula so as to maintain a consistent temperature profile from the first end of the injection cannula to the second end of the injection cannula, wherein the temperature profile comprises a temperature gradient from the first end of the injection cannula to the second end of the injection cannula and wherein the temperature gradient is warmer at the first end of the injection cannula than at the second end of the injection cannula.

5. The bone support attachment device of claim 4, wherein the actively regulated cannula heater comprises multiple heating elements.

6. The bone support attachment device of claim 4, wherein the actively regulated cannula heater comprises multiple thermal control circuits.

7. The bone support attachment device of claim 4, wherein the actively regulated cannula heater is configured to raise a temperature of the polymer within the injection cannula to a melting point of the polymer and is configured to actively control the temperature of the polymer at the second end of the injection cannula to a temperature that is low enough to not cause necrosis when the polymer is discharged from the injection cannula to contact tissue.

8. The bone support attachment device of claim 4, wherein the actively regulated cannula heater is configured to raise a temperature of the polymer within the injection cannula to between 50° C. and 250° C.

9. The bone support attachment device of claim 8, wherein the actively regulated cannula heater is configured to raise the temperature of the polymer within the injection cannula to between 130° C. and 180° C.

10. The bone support attachment device of claim 1, further comprising a depth gauge proximate the second end of the injection cannula, the depth gauge configured to move relative to the second end of the injection cannula once a predetermined volume of polymer is expelled from the second end of the injection cannula.

11. The bone support attachment device of claim 10, wherein the depth gauge is positionable configured as a static shelf and positioned at a selectable proximal distance from the second end of the injection cannula.

12. The bone support attachment device of claim 10, wherein the second end of the injection cannula is configured to extend a selectable distance from the depth gauge.

13. The bone support attachment device of claim 12 11, wherein the selectable proximal distance is greater than a thickness of a bone support such that when the bone support is engaged with a static shelf of the depth gauge, the second end of the injection cannula extends completely through the bone support.

14. The bone support attachment device of claim 1, wherein the actively regulated chamber heater is configured to raise a temperature of the polymer within the chamber to a melting point of the polymer and is configured to actively control the temperature of the polymer at the second end of the chamber to a temperature that is low enough to not cause necrosis when the polymer is discharged from the injection cannula to contact tissue permits the polymer to flow into the polymer supply inlet.

15. The bone support attachment device of claim 1, wherein the actively regulated chamber heater is configured to raise a temperature of a portion of the polymer within the chamber to between 50° C. and 250° C.

16. The bone support attachment device of claim 15, wherein the actively regulated chamber heater is configured to raise a temperature of a portion of the polymer within the chamber to between 130° C. and 180° C.

17. The bone support attachment device of claim 1, wherein a temperature at the second end of the injection cannula is controlled in a range within approximately 37° C. to 55° C.

18. The bone support attachment device of claim 1, wherein a starting plunger location is variable to provide a variable volume in the injection cannula that corresponds to a selectable amount of polymer to form fasteners of various sizes.

19. The bone support attachment device of claim 1, further comprising a chamber plunger configured to expel polymer from the chamber into the injection cannula when actuated.

20. The bone support attachment device of claim 1, wherein at least a portion of the plunger is configured to reduce adhesion of polymer to the plunger.

21. The bone support attachment device of claim 1, further comprising an actuator configured to advance the plunger at a rate sufficient for at least a portion of the polymer expelled from the injection cannula to interdigitate within a bone into which the injection cannula is extended.

22. The bone support attachment device of claim 1, further comprising an actuator configured to advance the plunger at a rate sufficient to form a bulbous polymer tip proximate a point distal to the second end of the injection cannula, the point distal to the second end of the injection cannula being defined by an inner cortical bone surface that is opposite a cortical bone surface upon which a bone support is positioned when the injection cannula is extended through the bone support during operation of the bone support attachment device.

23. The bone support attachment device of claim 1, wherein the plunger, when actuated, cuts off the supply inlet.

24. A bone support attachment device, comprising:

an injection cannula sized to hold a first amount of polymer to form a single fastener;

a polymer supply inlet coupled to a side of the injection cannula;

a plunger having a tip disposed at a first end of the injection cannula such that, when activated, the plunger expels the first amount of polymer from a second end of the injection cannula upon the plunger reaching the second end of the injection cannula;

a chamber sized to house a second amount of polymer sufficient to form a plurality of fasteners, the chamber having a first end having a chamber polymer supply inlet and a second end distal the first end and connected to the polymer supply inlet to sequentially provide the first amount of polymer to form a single fastener from the chamber; and,

a chamber heater, adjacent the chamber and configured to actively regulate the chamber so as to maintain a temperature profile from a first end of the chamber to the second end of the chamber, wherein the temperature profile comprises a temperature gradient from the first end of the chamber to a the second end of the chamber and wherein the temperature gradient is warmer at the second end of the chamber than at the first end of the chamber.

25. A bone support attachment device, comprising:

an injection cannula sized to hold an amount of polymer to form a single fastener;

a polymer supply inlet in fluid communication with a side of the injection cannula;

a plunger having a tip disposed at a first end of the injection cannula such that, when activated, the plunger expels the amount of polymer from a second end of the injection cannula upon the plunger reaching the second end of the injection cannula;

a chamber sized to house a supply of polymer sufficient to form a plurality of fasteners, the chamber having a first end having a chamber polymer supply inlet and a second end distal the first end and in fluid communication with the polymer supply inlet to sequentially provide the amount of polymer to form a single fastener from the chamber; and,

a chamber heater, adjacent the chamber and configured to actively regulate the chamber so as to maintain a temperature profile from a first end of the chamber to the second end of the chamber, wherein the temperature profile comprises a temperature gradient from the first end of the chamber to a the second end of the chamber and wherein the temperature gradient is such that the polymer is warmer at the second end of the chamber than at the first end of the chamber.

26. A bone support attachment device for forming fasteners from a polymer composition, the bone support attachment device comprising:

an outer device body having a proximal portion, a distal end, and a distal tip portion located proximally from and adjacent to the distal end, the outer device body having a bore located at the distal end;

an injection cannula extending through the bore and having a first end located within the outer device body and a second end located distally from the bore of the device body, the injection cannula also having a polymer supply inlet through a side of the injection cannula;

a polymer supply chamber having an inlet end and a discharge end in fluid communication with the inlet end and with the injection cannula through the polymer supply inlet;

a plunger having a plunger tip configured to be disposed within the injection cannula and to be movable within the injection cannula from the first end to the second end; and

a chamber heater adjacent the polymer supply chamber configured to actively maintain a rising temperature gradient for a polymer composition within the polymer supply chamber, wherein the rising temperature gradient is such that a temperature of the polymer composition at the inlet end is less than a temperature of the polymer composition at the discharge end of the polymer supply chamber.

27. The bone support attachment device of claim 26 wherein the injection cannula has a proximal portion adjacent the first end and wherein a maximum outer dimension of the plunger tip is from 2 to 200 μm less than a minimum inner dimension of inner walls of the injection cannula at the proximal portion of the injection cannula.

28. The bone support attachment device of claim 27, wherein the injection cannula has a distal portion adjacent the second end and wherein the plunger tip forms an interference fit with inner walls of the injection cannula at the distal portion of the injection cannula.

29. The bone support attachment device of claim 26 further comprising a quantity of a thermoplastic polymer composition that is non-flowable at room temperature located within the polymer supply chamber.

30. The bone support attachment device of claim 29 wherein the thermoplastic polymer composition comprises an aliphatic polyester.

31. The bone support attachment device of claim 30 wherein the aliphatic polyester comprises a homo- or co-polymer of polylactic acid, polyglycolic acid, or polycaprolactone.

32. The bone support attachment device of claim 29 wherein the thermoplastic polymer composition comprises polylactide/polyglycolide.

33. The bone support attachment device of claim 32 wherein the rising temperature gradient is sufficient to transition the thermoplastic polymer composition from a non-flowable state to a temperature up to or above the melting point of the thermoplastic polymer composition.

34. The bone support attachment device of claim 29, wherein the thermoplastic polymer composition includes a therapeutic agent.

35. The bone support attachment device of claim 34, wherein the therapeutic agent comprises an antibiotic.

36. A bone support attachment device for forming fasteners from a polymer composition, the bone support attachment device comprising:

an outer device body having a proximal portion, a distal end, and a distal tip portion located proximally from and adjacent to the distal end, the outer device body having a bore located at the distal end;

an injection cannula extending through the bore and having a first end located within the outer device body and a second end located distally from the bore of the device body, the injection cannula also having a polymer supply inlet through a side of the injection cannula;

a polymer supply chamber having an inlet end and a discharge end in fluid communication with the inlet end and with the injection cannula through the polymer supply inlet;

a plunger having a plunger tip configured to be disposed within the injection cannula and to be movable within the injection cannula from the first end to the second end;

a cannula heater disposed at the distal tip portion configured to actively maintain a decreasing temperature gradient for a polymer composition within the injection cannula, wherein the decreasing temperature gradient is such that a first temperature of the polymer composition at a first position of the second end of the injection cannula is lower than a second temperature of the polymer composition at a second position located proximally from the first position within the injection cannula; and,

means for dissipating heat from a distal portion of the injection cannula.

37. The bone support attachment device of claim 36 wherein the injection cannula has a proximal portion adjacent the first end and wherein a maximum outer dimension of the plunger tip is from 2 to 200 μm less than a minimum inner dimension of inner walls of the injection cannula at the proximal portion of the injection cannula.

38. The bone support attachment device of claim 37, wherein the injection cannula has a distal portion adjacent the second end and wherein the plunger tip forms an interference fit with inner walls of the injection cannula at the distal portion of the injection cannula.

39. The bone support attachment device of claim 36 further comprising a quantity of a thermoplastic polymer composition that is non-flowable at room temperature located within the polymer supply chamber.

40. The bone support attachment device of claim 39 wherein the thermoplastic polymer composition comprises an aliphatic polyester.

41. The bone support attachment device of claim 40 wherein the aliphatic polyester comprises a homo- or co-polymer of polylactic acid, polyglycolic acid, or polycaprolactone.

42. The bone support attachment device of claim 39 wherein the thermoplastic polymer composition comprises a polylactide/polyglycolide polymer.

43. The bone support attachment device of claim 42 wherein the decreasing temperature gradient is sufficient to maintain the thermoplastic polymer composition in a flowable state.

44. The bone support attachment device of claim 39, wherein the thermoplastic polymer composition includes a therapeutic agent.

45. The bone support attachment device of claim 44, wherein the therapeutic agent comprises an antibiotic.

46. A bone support attachment device for forming fasteners from a polymer composition, the bone support attachment device comprising:

an outer device body having a proximal portion, a distal end, and a distal tip portion located proximally from and adjacent to the distal end, the outer device body having a bore located at the distal end;

an injection cannula extending through the bore and having a first end located within the outer device body and a second end located distally from the bore of the device body, the injection cannula also having a polymer supply inlet through a side of the injection cannula;

a plunger having a plunger tip configured to be disposed within the injection cannula and to be movable within the injection cannula from the first end to the second end;

a polymer supply cartridge containing an amount of thermoplastic bioresorbable polymer, the polymer supply cartridge being removably attached to the outer device body and having a distal discharge opening in fluid communication with the injection cannula;

a heater located proximate the distal tip portion of the outer device body, wherein the heater is configured to actively regulate the temperature of the thermoplastic bioresorbable polymer in the injection cannula so as to maintain a temperature profile within the injection cannula;

wherein the temperature profile comprises a decreasing temperature gradient such that a first temperature of the thermoplastic bioresorbable polymer at a first position at the second end of the injection cannula is lower than a second temperature of the thermoplastic bioresorbable polymer at a second position located proximally from the first position within the injection cannula.

47. The bone support attachment device of claim 46, wherein the thermoplastic bioresorbable polymer comprises an aliphatic polyester.

48. The bone support attachment device of claim 47, wherein the aliphatic polyester comprises a homo- or co-polymer of polylactic acid, polyglycolic acid, or polycaprolactone.

49. The bone support attachment device of claim 48, wherein the co-polymer is polylactide/polyglycolide.

50. The bone support attachment device of claim 46, wherein the thermoplastic bioresorbable polymer includes a therapeutic agent.

51. The bone support attachment device of claim 50, wherein the therapeutic agent comprises an antibiotic.