Abstract:
A heating device for maintaining an elevated temperature of a polymer resorbable implant is disclosed. The heating device has a pair of members coupled by a hinge. At least one of the members defines a sealed cavity containing a heated liquid which maintains the temperature of the resorbable polymer implant above the implant&#39;s glass transition temperature. The members of the device being rotatable about a hinge to allow encapsulation of the resorbable implant adjacent to the heat bearing liquid while maintaining a separation between the liquid and the implant device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to an apparatus and method for heating a resorbable implant, and more particularly, to a method and apparatus for heating a resorbable implant which is reusable and provides a method for heating to thereby soften the resorbable implant prior to surgical implantation. 
     2. Discussion of the Related Art 
     The repair of separated or dislocated bone fragments or segments following bone surgeries sometimes requires realignment of the separated or dislocated fragments or segments and subsequent secure fixation for promoting proper natural rejoinder of these bone fragments or segments. The presence of relative motion of the bone fragments or segments at a fracture or osteotomy location may result in irritation of the surrounding tissues, nonunion between the bone fragments, and an extension of the time for fracture healing. It is therefore desirable to accomplish as completely as possible an immobilization of the fracture or osteotomy site. This involves the relative fixation of affected bone segments relative to each other and in relation to the surrounding bone structure. 
     Known methods for providing fixation between adjacent bone portions have included the use of metallic plates of varying configurations, which are secured across osteotomies or fracture sites by metallic bone screws. These devices have been made of biocompatible metals and metal alloys, such as commercially pure titanium, stainless steel and cobalt chrome molybdenum. Other materials and devices, such as wires, intramedullary nails or externally fixed pins have also been used to reduce bone fracture mobility and to improve the relative position of adjacent segments. The aim of fixation of adjacent bone portions is to immobilize the fracture or osteotomy sites in order to promote localized bone growth in the natural repair of the separation. 
     The use of medical implant devices made from bioresorbable materials has been described in literature and these devices have the advantage of being absorbed by the body over a period of time so as to allow for bone or fibrous material to become repaired at a fracture or osteotomy site by growing into the space created between adjacent bone portions. Many bioresorbable materials have been suggested for use in fixation of adjacent bone portions. It was believed that these materials had to be extremely strong to fixate the bone portions over a relatively long period of time. This typically meant that the osteosynthesis plate had to be relatively thick and be made out of a high molecular weight oriented material such as poly L-lactic acid in which the molecular weight would exceed 250,000. See Pihlajamaki, H., et al., “Absorbable Pins of Self-Reinforced Poly-L-Lactic Acid for Fixation of Fractures and Osteotomies,” Journal of Bone and Joint Surgery, v. 74-B, n. 6, p. 853-857, November 1992. In addition, it was believed that certain copolymers of glycolide and lactide were not appropriate for use in osteosynthesis plates because of a rapid loss of mechanical strength. Grijpma, D. W., et al., “Poly (L-lactide) Crosslinked with Spiro-bis-dimethylene-carbonate,” Polymer, v. 34, n. 7, 1993 at 1496. 
     One resorbable material of particular interest is marketed by Biomet, Inc. (Warsaw, Ind.) under the tradename LACTOSORB®. LACTOSORB® is an absorbable co-polymer synthesized from all-natural ingredients: 82% L-lactic acid and 18% glycolic acid, unlike the homopolymers in common use such as 100% poly-L-lactic acid (PLLA) or 100% poly-glycolic acid (PGA), LACTOSORB® copolymer is substantially amorphous (i.e., without crystallinity), meaning that its degradation is uniform, precluding the crystalline release associated with degrading copolymers that have been associated with late inflammatory reactions. Furthermore, the LACTOSORB® copolymer ratio permits the polymer to retain most of it&#39;s strength for six to eight weeks, which is appropriate for healing, but not so long as to raise concerns about long-term stress shielding of bone. 
     These polymeric resorbable devices may require “molding in the operating room” before they can be implanted. By way of non-limiting example, the minimum temperature for achieving a moldable condition generally is above the glass transition temperature (Tg) (approximately 57/60° C.). During the heating stages of the resorbable materials, it is best not to allow the device (or any device possibly affected by water) to come in direct contact with boiling water. Because of this, It is difficult to raise the temperature of the resorbable device to above its glass transition temperature and to maintain the device above its glass transition temperature for long enough periods of time in the operating room to allow interoperative implant shape changes. 
     A need, therefore, exists for an apparatus and system which can raise a resorptive polymer material implant to above its glass transition temperature without exposing the implant directly to a liquid phase material. A need further exists for an apparatus and system which allows the resorbable material to be maintained above its glass transition temperature for an extended period of time. Further, a need exists for a heating device which is sterilizeable, as well as resusable. 
     SUMMARY OF THE INVENTION 
     In accordance with the teaching of the present invention, a device capable of heating resorbable material is disclosed having a pair of generally planar members. Each planar member defines at least one cavity which contains heatable fluid. The generally planar members are coupled by a hinge which allow the members to be rotated adjacent to each other so as to hold the resorbable polymer implant in close proximity to the heatable fluid. The temperature of the liquid stored within the cavity is elevated to above the glass transition temperature of a resorbable polymer. The resorbable polymer component which is to be surgically implanted in a patient is placed between the folded members and absorbs heat from the liquid stored within the cavity. 
     In one preferred embodiment, each member defines a shallow dish portion. Disposed above the shallow dish portion is a flexible polymer member which defines a fluid filled cavity therebetween. The fluid filled cavities are disposed adjacent to each other when the members are folded about the hinge, thereby holding the resorbable polymer component between two flexible polymer members, thereby increasing the surface area of the component in close proximity to the liquid. 
     In yet another preferred embodiment, the members define a cavity which is capable of accepting a fluid filled bag into a slot. The fluid filled bags can be heated prior to incorporation into the members through the slot. 
     In yet another preferred embodiment, the fluid filled bags are fastened to one surface of the foldable members using standard fabric fasteners. As with the other system, the fluid filled bag may be heated either prior to or after its adjoinment with the members. 
     The present invention provides a device which is capable of heating a resorbable surgical component and maintaining it above its glass transition temperature. The devices contain at least one fluid filled flexible sack, which functions to store heat energy to be transferred to the resorbable material through the flexible sack without submerging the resorbable material in a liquid. As a result, the aforementioned disadvantages associated with currently available resorbable material heating systems have been substantially reduced or eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will be apparent to one skilled in the art upon reading the following specifications and by reference to the drawings in which: 
     FIGS. 1-4 represent the resorbable implant heating device of the current invention; 
     FIGS. 5-7 represent a second embodiment of the resorbable implant heating device of the current invention; 
     FIGS. 8-9 represent yet another embodiment of the present invention; and 
     FIGS. 10-11 represent the incorporation of a polymer device into the resorbable implant heating device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Moreover, while various specific structures are disclosed, it will be understood by those skilled in the art that they are merely exemplary and other specific structures may be used. 
     FIGS. 1-3 disclose a first embodiment of a resorbable implant heating device  10  of the present invention. The resorbable implant heating device  10  is formed of a first member  12  and second member  13  which are coupled by a hinge  11 . Disposed on a first and second surface  14  and  15  of the first and second members  12  and  13  are first and second fluidized compartments  16  and  17 . The fluidized compartments  16  and  17  are formed by a first and second elastic or flexible members  18  and  20  and first and second concave surface  22  and  24  which are disposed within the first and second surfaces  14  and  15 . The first and second elastic or flexible members  18  and  20  are sealed to the perimeter of the generally concave surfaces to form a cavity to encapsulate a liquid which is saline or another appropriate liquid. Further disposed within the first and second members  12  and  13  are a pair of handles  26  which are used to carry the resorbable implant heating device  10  during a surgical procedure. Defined on the first and second surface  14  and  15  are a plurality of fastening devices  21  to hold the first and second surfaces  14  and  15  together and generally parallel to each other after rotating about hinge  11 . Shown are male and female components  28  and  30  of the fastening devices  21 . It should be envisioned that any other coupling structure such as a hook and eye, snap, VELCRO®, etc. would be equally applicable. 
     FIG. 4 depicts the use of the resorbable implant heating device  10  as contemplated. As shown, the first member  12  is rotated about hinge  11  so the first and second fluidized compartments  16  and  17  are disposed adjacent to each other. Located between the first and second elastic or flexible members  18  and  20  is the resorbable polymer implant  32  to be heated. It is envisioned that the entire resorbable implant heating device  10  can be placed into an autoclave or microwave or other heating apparatus to bring the fluid which is stored within the first and second fluidized compartments  16  and  17  up above the glass transition temperature of the resorbable polymer implant  32 . Either prior to or after the heating of the liquid, the resorbable implant  32  is placed onto the second elastic membrane  20  and the first member  12  is rotated about hinge  11  into place. Upon encountering the second member  13 , the female portion  30  of the fastener  21  is coupled to the male portion  28  to lock the two devices together. As can be seen, the handles  26  facilitate easy movement of the resorbable implant heating device  10  about the operating room. 
     FIGS. 5-7 depict another preferred embodiment of the present invention. As shown in FIG. 5, the resorbable implant heating device  40  has a pair of generally planar members  42  and  43  coupled together by hinge  44 . Similar to the device shown in FIGS. 1-4, the members  42  and  43  can define a pair of handles  26  for ease of movement of the device  40 . Shown is a VELCRO® fastener  56  which can be used to adjustably fasten the handles together. 
     FIG. 6 depicts a cross-section of the resorbable implant heating device  40 . As is shown, the first member  42  has a inner surface  45  and an outer surface  46 . Defined between the inner and outer surfaces  45  and  46  is a cavity  47 . The cavity  47  is accessible, via slot  48 , defined in the inner surface  45 . Disposed within the cavity  47  is a fluid filled bag  50 . Optionally, similar structures can be defined in member  43 . Further depicted are the inner surface  51  and outer surface  52 . Defined between the surfaces  51  and  52  is the cavity  53  which holds a fluid filled bag  55 . As can be seen in FIG. 7, the fluid filled bag  55  can be inserted into the structure through slot  54  defined in the first surface  51 . 
     FIGS. 8-9 depict yet another embodiment of the present invention. Shown is a resorbable implant heating device  60  having first and second halves  62  and  64  separated by a hinge mechanism  65 . Each of the members  62  and  64  has a plurality of fastening devices  66  which couple to fastening devices  67  on the fluidized bag  68 . While it is envisioned that the non-implant conducting surfaces of the first and second members  12  and  13  would have insulating properties, FIG. 9 shows a lower surface  69  having a layer of insulating material  70  to assist in the retention of heat in the resorbable implant heating device. 
     It is envisioned that the elastic members  18  and  20  of resorbable implant heating device  10 , the fluid filled bag  55  of the heating device  40 , and the fluidized bag  68  of heating device  60  be formed of a autoclavable material which remains flexible such as silicone. It is preferable that the liquid stored beneath these layers have a high boiling point of greater than about 220° F. and a high specific heat. It is further preferable that the contact surface of each heating device in relation to the implant be configured of a material having a high heat transfer coefficient. The resorbable implant heating devices  10 ,  40 , or  60  could each be inserted into an autoclave or a microwave generating device to heat the fluid within. The structural material of the first and second members  12  and  13  or  42  and  43  for either resorbable implant heating device  10  or  40  can be made of a relatively rigid insulating material to trap the heat within the fluidized compartments  16  and  17  or  47  and  53 . 
     Insertion of the resorbable polymer implant  32  is depicted in FIGS. 10-11. In practice, the resorbable implant heating devices  10 ,  40 , and  60  could each be placed within an autoclave until needed. After insertion of the resorbable polymer implant  32 , the resorbable implant heating device  10 ,  40 , or  60  is closed about the resorbable polymer implant  32 . The resorbable implant heating device  10 ,  40 , or  60  can additionally be wrapped in towels to maintain the heat. It should also be noted that the implant  32  may be positioned within the heating devices  10 ,  40 , and  60  before the heating device is heated. It should also be noted that the heating device  10 ,  40 , or  60  may eliminate its corresponding hinge such that each member of the heating device is separate and subsequently attached, via the fastening devices. 
     A wide variety of features can be utilized in the various materials disclosed and described above. The foregoing discussion discloses and describes a preferred embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications, and variations can be made therein without departing from the true spirit and fair scope of the invention.