Abstract:
A method for spreading skin grafts, wherein the skin grafts are placed on an elastic membrane, after which the membrane is stretched in at least two directions substantially perpendicular to each other and the skin grafts present on the membrane are spread. A spreading means, a stretcher and a membrane to be used therewith, as well as to a method for applying skin grafts to a burn.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for spreading skin grafts and to spreading means, a stretcher and a membrane to be used therewith, as well as to a method for applying skin grafts to a burn. 
     BACKGROUND OF THE INVENTION 
     In practice a method for spreading skin grafts often comprises placing skin grafts on gauze which has been pre-folded in two directions in advance (pleat). To that end an adhesive is applied to the skin grafts on the pre-folded gauze, and after the adhesive has dried the folded gauze is stretched in two directions, as a result of which the distance between the skin grafts is increased. This has led to the situation wherein the small squares, viz. the cut skin grafts, are arranged in regularly spaced-apart (about 5 mm) relationship, with the cutting side facing upwards. Then the folded bandage is laid loosely on the excided area, provided with perforations for drainage, and subsequently fixed in position by means of gauze. In this manner an increase in area of about nine times the original dimension is obtained. The drawback of such a method is that after about one week the gauze is removed under an anaesthetic and can be replaced by donor skin. Another drawback is the fact that it takes a considerable amount of routine to be able to carry out such a method. In addition to that the use of an adhesive is undesirable, because it has an adverse effect on the production of large amounts of skin grafts. 
     In addition to that it is known from International patent application WO 92/15251 to stretch skin, using stretching means to be fitted to a patient under local anaesthesia. The extra skin which is formed by said stretching in conjunction with the natural growing power of the human skin is cut away and used for transplantation purposes. A drawback of such a method is the fact that it takes surgery to obtain additional skin. 
     SUMMARY OF THE INVENTION 
     Now a method for spreading skin grafts has been found which does not exhibit the above drawbacks. In addition to that the method which has been discovered can be carried out by medical staff who have not been specially trained for this purpose. 
     The method as referred to in the introduction is characterized in that the skin grafts are placed on an elastic membrane, after which the membrane is stretched in at least two directions substantially perpendicular to each other and the skin grafts present on the membrane are spread. 
     A method for forming skin grafts is known from Dutch patent application No. 1004276, which document may be considered to be incorporated herein. Although it is possible to use any other known method for forming skin grafts, such as the method known from International patent application WO 84/02464, it is preferred to use the method according to Dutch patent application No. 1004276. 
     It is preferred to use as a membrane a carrier which is used for forming the skin grafts. According to this method an increase in area of about nine times the original dimension is achieved. From practice it has become apparent that in this manner little auto transplant or autogenous skin is needed to cover large defects on burn patients. 
     The present invention furthermore relates to spreading means to be used for increasing the distance between the skin grafts, which means is characterized in that said spreading means comprises an elastic membrane which is connected to arms which are capable of movement in at least two directions in the same plane, which arms are made of a material which is less elastic than the material of which the membrane is made, as well as a base member, which can be connected to said arms. 
     In a preferred embodiment said spreading means comprises four to eight arms which are capable of movement in opposite directions in the same plane, which arms can be connected to the base member, after which the arms are extended. Since the material of which the membrane is made is more elastic than the material of which the arms are made, the surface area of the membrane will be considerably extended as a result of the extension of the arms. Thus the distance between the skin grafts will be increased and the spreading of the skin grafts has been achieved. 
     In a special embodiment of the present invention the skin grafts formed from skin, which adhere to a carrier, are transferred to the elastic membrane of the spreading means by transport means operating at a sub-atmospheric or reduced pressure. A transport means operating at a sub-atmospheric pressure is known from International patent application WO 84/02464. The skin grafts adhering to the transport means are removed therefrom by releasing the sub-atmospheric pressure, possibly in conjunction with the moving of pins from an ejector through the apertures of the transport means, or by applying a slight overpressure by using compressed air, after which the skin grafts land on the membrane, in particular on the central part thereof. Then the elastic membrane is stretched by moving the arms of the assembly of membrane and arms, which is according to the present invention preferably carried out by using wind-up means connected to the base member, which wind-up means are rotatably mounted therein. Such wind-up means can be connected to the arms, as a result of which the membrane connected to the arms can be stretched and the skin grafts present on the membrane can be spread. The assembly of membrane and arms is preferably moved by connecting the arms to the base member via wind-up rods, which wind-up rods can be moved by means of a ratchet wrench and a gear wheel, for example. Further extension of the membrane by means of such wind-up rods, whereby the arms are wound on the wind-up rods, will result in the distance between the skin grafts being increased. In certain embodiments of the present invention the arms may already be attached to the base member, however, and the membrane may have to be connected to the arms so as to spread the skin grafts present on the membrane. The advantage of this is that the membrane can be disposed of after use and be replaced by a new membrane. If the membrane and the arms are made in one piece, the arms must be connected to the wind-up rods, and the assembly of membrane and arms can be removed and be replaced after use. 
     It is preferred to make the membrane of an elastic material having a rough surface or porous material in order to ensure a minimal adherence of the skin grafts to the membrane. A woven or knit material is suitable as the porous material for the membrane. The advantage of a material of this type is that when a force is exerted thereon, the yarns are pulled apart, as a result of which the desired space between the yarns, or the desired porosity, is achieved. In addition to that it must be possible to subject the membrane to a sterilization treatment. In a special embodiment of the spreading means the space under the membrane is provided with a connection for sub-atmospheric pressure and compressed air. Preferably also an ejector is mounted in such a space. It should be apparent that spread skin grafts can be removed from the spreading means by tweezers, but this is very time-consuming, and in practice it is preferred to use the transport means described in Dutch patent application No. 1004276. 
     In a special embodiment of the spreading means according to the present invention a stretcher is provided, which can be connected to the base member. The arms of the elastic membrane can be clamped down in such a stretcher, thus making it possible to maintain the stretched condition of the arms, which is obtained by stretching the arms, using the above-described wind-up means. Thus the stretcher with the spread skin grafts present on the membrane can be detached from the base member and be transported to the intended location. The base member will then be available again for spreading a new batch of skin grafts in accordance with the method of the present invention. The advantage of using such a stretcher is that large amounts of spread skin grafts can be obtained at short intervals, in particular by using only one base member. 
     In a preferred embodiment of the present invention the stretcher to be used in spreading skin grafts comprises at least two clamping means, in which the membrane and/or the arms connected to the membrane can be clamped down. More in particular the number of arms connected to the membrane corresponds with the number of clamping means present in the stretcher, preferably the number of clamping means is four to eight. The clamping means according to the present invention preferably comprises a base member and a top member, whereby said base member and said top member exhibit a clamping action. 
     The present invention furthermore relates to a method for applying skin grafts to a burn, which method is characterized in that a skin-like material is placed on the spread skin grafts, after which the skin grafts adhering to said material are applied to the burn. Preferably a gauze of plastic material is used as a suitable skin-like material. More in particular donor skin is used. When the skin grafts are covered with donor skin, the healing process is accelerated, which is desirable in practice. 
     In another embodiment an adhesive is first applied to the spread skin grafts, after which a skin-like material is placed on the skin grafts provided with an adhesive, and the whole is subsequently applied to the burn. The advantage of applying an adhesive is that the spread skin grafts adhere to the material in an advantageous manner, as a result of which no skin grafts are lost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be explained in more detail hereafter by means of the appended examples in conjunction with the illustrated drawings. 
     FIG. 1 shows the membrane connected to the arms according to the present invention, which can be used for increasing the distance between the skin grafts. 
     FIG. 2 shows the base member of the spreading means according to the present invention. 
     FIG. 3A shows the stretcher to be used in spreading skin grafts according to the present invention. 
     FIG. 3B shows the clamping means according to the stretcher as shown in FIG.  3 A. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the elastic membrane  18  to be used in spreading skin grafts in accordance with the method of the present invention. Assembly  20  comprises an elastic membrane  18 , which is connected to eight arms  17  capable of movement in opposite directions in the same plane. The skin cut into skin grafts is transferred to elastic membrane  18 . Once the skin grafts are present on elastic membrane  18  of assembly  20 , the distance between the skin grafts is increased by moving arms  17  in opposite directions in the same plane, which is done by connecting arms  17  to cam  38  present on wind-up rod  39  of base member  40  shown in FIG. 2, using hole or aperture  37 . The term spreading means is understood to mean the whole of assembly  20  and base member  40 . 
     Base member  40  can be connected to assembly  20 , which comprises arms  17  and membrane  18 , whereby arm  17  is provided with hole  37 , by placing hole  37  over a wind-up rod  39  provided with a cam  38 . Base member  40  comprises a number of wind-up rods  39 , which wind-up rods  39  are interconnected via connecting point  41 . Rotating means  43 , for example a ratchet wrench, can be rotated in the direction of the arrow shown in FIG. 2, causing the gear wheel  44  connected to rotating means  43  to drive wind-up rods  39 . Locking member  42 , which is connected to gear wheel  44 , ensures that wind-up rods  39  remain in the desired position. The assembly  20  shown in FIG. 1 is placed on base  45  of base member  40 , whereby holes  37  of arms  17  are connected to cam  38  of each wind-up rod  39 . Rotation of rotating means  43  will result in arms  17 , which are connected to wind-up rod  39  by means of hole  37  and cam  38 , being wound on wind-up rod  39 , as a result of which a force will be exerted on the assembly  20  of membrane  18  and arms  17 . The exertion of this force on assembly  20  leads to the more elastic membrane  18  being stretched, as a result of which the distance between the skin grafts present on membrane  18  is increased. 
     FIG. 3A shows the stretcher  200  to be used in spreading skin grafts. Stretcher  200  comprises a frame  201 , in which clamping means  202  are arranged in regularly spaced-apart relationship. According to such an embodiment membrane  18 , which is connected to arms  17 , can be stretched in stretcher  200  by passing arms  17  through the clamping means  202  shown in FIG.  3 B. Clamping means  202  comprises a base part  203  and a top part  204 . When arm  17  is passed between base part  203  and top part  204  of clamping means  202 , a particular clamping action is obtained as a result of the friction between the two parts, and the stretched condition of the assembly of membrane  18  and arms  17  will be retained. Stretcher  200  is placed on base member  40 , arms  17  are passed between base part  203  and top part  204 , hole  37  is connected to cam  38  of each wind-up rod  39 , and then a spreading action as already described before is carried out. After achieving a sufficient spreading effect stretcher  200  is removed from base member  40  and clamping means  202  ensure that the stretched condition in stretcher  200  is retained. Then another stretcher  200  is placed on base member  40  and a number of skin grafts are spread in accordance with the above-described operation. 
     Once a desired distance between the skin grafts on elastic membrane  18  has been achieved, the skin grafts are transported, using a transport means operating at a sub-atmospheric pressure, for example. Said transport means is held with the side of apertured plate above the spread skin grafts present on the spreading means, after which a sub-atmospheric pressure is applied to the holding means by suitably adjusting the position of a changeover cock, which causes the skin grafts to adhere to the apertured plate. Then the skin grafts are then transported, for example to a burn, by the transport means. In a special embodiment a gauze of plastic material, more preferably donor skin, is provided over the spread skin grafts, which have been applied to a burn. In a special embodiment an adhesive is used in order to improve the adherence between the spread skin grafts and the material to be adhered. It is also possible, however, to transport spread skin grafts by means of tweezers, but it should be apparent that transporting each skin graft separately by means of tweezers is a very time-consuming activity. The number of skin grafts to be used with a burn generally amounts to a few dozen, so that it is preferred to transport the skin grafts by the above-described transport means. 
     Based on their experience and insight those skilled in this field are convinced that the healing process of a burn to which the skin grafts spread in accordance with the present invention have been applied, covered by donor skin, can be reduced by one week in comparison with the healing period obtained with the prior art methods.