Abstract:
An instrument for stretching tissue is provided. The instrument can include opposing hook jaws  10  movably coupled to a rod  12  and movable toward each other, and each hook jaw  10  can have a hook receptacle  18.  A hook module  20,  having at least one hook  22,  can be seated in the hook receptacle  18.  An adjustment cam  28  can be connected to each hook module  20  and an adjustment drive  26  can be coupled to the adjustment cams  28  where the adjustment drive  26  moves the adjustment cams  28  to cause a skin stretching force at one or more hook modules  20  and to cause a skin reperfusion force at one or more hook modules  20.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 11/738,268 filed Apr. 20, 2007, which was a divisional application of U.S. patent application Ser. No. 10/378,518, filed Mar. 3, 2003, now U.S. Pat. No. 7,208,006, issued Apr. 24, 2007, which claims the benefit of German Patent Application No. DE 102 09 122.6 filed Mar. 1, 2002, the entirety of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention concerns a process and an instrument for stretching tissue of skin. 
         [0004]    2. Description of the Related Art 
         [0005]    For closing large wounds and skin defects it is known from, for example, U.S. Pat. No. 5,486,196 and U.S. Pat. No. 5,618,310 to mechanically stretch the skin surrounding the wound or the skin defect, thereby inducing accelerated tissue regeneration. Distractors are employed for this skin stretching, which are anchored in the skin and include pulling means. These pulling means transmit a pulling force to the skin tissue for stretching the skin. A higher pull force brings about a stronger tissue proliferation. A high pull force however also has as a consequence that on the pressure side, ahead of the pull means, the skin tissue is compressed. In the instrument known from U.S. Pat. No. 5,486,196 the pull force is transmitted to the skin tissue via a long inter-dermal needle, which is anchored in the skin parallel to the edge of the wound. Thereby higher pull forces can be transmitted to skin tissue, without the pressure on the pressure side of the long needle rising above a critical closure pressure of the tissue system, which could lead to ischemia of the tissue. In the case of the instrument disclosed in U.S. Pat. No. 5,618,310 the pull force is introduced via a needle stuck into the skin at one point. Accordingly, the pull force is limited such that the critical closure pressure which could lead to ischemia on the pressure side of the needle is not exceeded. This limitation on the pull force also means a limitation on the stretching of the skin, so that an optimal tissue new formation is not achieved. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is concerned with the task of providing a process and an instrument via which, for the stretching of the tissue of the skin, a high pull force can be introduced point wise into skin without the pull means causing damage of the tissue on the pressure side. 
         [0007]    Preferred embodiments of the invention are disclosed in the respective dependent claims. 
         [0008]    The essential idea of the invention is comprised therein, that a cyclic alternating pull force is introduced into the skin via the pull means anchored at a point in the skin. Therein the pull force preferably alternates between two different values. The first value of the pull force is selected to be as large as possible, in order to stimulate a high as possible tissue new formation. This first value of the pull force is limited in its upper value essentially only by the resistance to tear of the skin. The first value is thus selected to be so high, that on the pressure side of the pull force the critical closure pressure of the venous capillary system of the skin is exceeded and thus ischemia is caused. This high pull force is maintained for a period of time which is within the ischemia tolerance duration of the skin tissue. Any duration of ischemia longer than this tolerance duration leads to a pressure induced dying of the skin tissue and therewith to a necrosis on the pressure side of the pull means. The ischemia tolerance duration of skin tissue is approximately 6 to 7 hours. Prior to reaching this ischemia tolerance duration, at which necrosis of the skin tissue is to be feared on the pressure side of the pull means, the pull force is reduced to a second value, which is so selected that the pressure exercised on the tissue on the pressure side of the pull means lies below the critical closure pressure of approximately 20-40 mm Hg. As a result of the pressure reduction the tissue is freed again ahead of the pull means for blood perfusion in the tissue and a rapid maximal reperfusion of the tissue occurs. This reperfusion occurs already after approximately 15 seconds, so that after approximately 0.5 to 5 minutes a complete perfusion and blood flow through the tissue on the pressure side of the pull means is ensured and the pull force can again be brought to the first high value. As a result of this cyclic change of the pull force a very high pull force for the tissue stretching of the skin can be employed for a prolonged duration of up to several days without the occurrence of a damaging of the skin and in particular a necrosis of the tissue on the pressure side of the pull means. The process and the instrument are thus suited in particular for the prolonged skin distraction for closure of large surface area skin defects. 
         [0009]    In a preferred embodiment of the invention two groups of pull means are anchored in the skin, wherein the pull means of the two groups are arranged alternatingly side-by-side and preferably in a row transverse to the direction of the pull force. Via the first group of the pull means the first high pull force is introduced into the skin, during which time the second group of pull means is relaxed and introduces the second—lower—pull force. The two groups of pull means thereby alternate periodically over time in the value of their pull force, wherein the periodicity of the change-over is smaller than the ischemia tolerance of the skin tissue. Thereby continuously the maximal pull force is exercised upon the skin by one of the groups of the pull means, so that the optimal pull force for tissue regeneration is exercised without interruption. On the other hand, the pull force is respectively alternatingly relaxed, so that the tissue on the pressure side of the pull means can respectively regenerate completely during this relaxation phase. 
         [0010]    In an advantageous design the pull means are in the form of hooks, which are stuck into the skin. In this case the hooks are in the form of hook modules in a hook receptacle, wherein the hook receptacle receives at least two hook modules, so that respectively at least one hook is available for each of the two groups. The hook modules in the hook receptacles are advanced preferably alternatingly by suitable adjusting means in the direction of the pull force. On the hook receptacles a high pull force with the first value is continuously exercised. This pull force is introduced into the skin via the hooks of the respective advanced hook module. The hooks of the respective non-advanced hook module is in this manner relaxed. The relaxed hook module is retracted by the elasticity of the skin until it no longer exercises any substantial pull force upon the skin. Alternatively the relaxed hook module can be pulled back by a spring force. It is likewise also possible to retract the relaxed hook module by positive control means. 
         [0011]    The repositioning of the hook module, that is the advancing of the hook module exercising the pull force and the releasing or in the case may be the drawing back of the released hook module can occur in various ways. Since with regard to the ischemia tolerance duration of approximately 6 to 7 hours, it can be calculated that if the alternation between the two groups of pull means should be carried out in time intervals of several hours, a simple manual adjustment would be practicable. For an automated long duration treatment the adjustment can be carried out using an electric motor or a pneumatic means, which are adapted to be automatically controlled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]    In the following the invention will be described in greater detail on the basis of the illustrative embodiments represented in the figures. There is shown 
           [0013]      FIG. 1  a side view of an instrument according to the invention, 
           [0014]      FIG. 2  a section along the line A-A in  FIG. 1 , 
           [0015]      FIG. 3  a view of a hook receptacle according to  FIG. 2  in a second embodiment, 
           [0016]      FIG. 4  a section along the line B-B in  FIG. 3  and 
           [0017]      FIG. 5  a representation according to  FIGS. 2 and 3  of a hook receptacle in a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    In  FIG. 1  an instrument for stretching the tissue of the skin, a so-called skin distractor, is shown. The basic construction of such a skin distractor as such as known and described for example in U.S. Pat. No. 5,486,196 or DE 44 44 130 A1. The skin distractor comprises two jaws  10 , which can be advanced towards each other using suitable adjusting means. The jaws  10  and the adjusting means are only schematically indicated in  FIG. 1 . The adjusting means could comprise for example a threaded spindle  12 , which is driven via a drive  14 . The drive  14  could be a manually operable knob or an automated motor drive. The jaws  10  are in this case seated via threaded boxes  16  on the threaded spindle  12 . The threaded boxes  16  exhibit counter-rotating threads, so that during a rotation of the threaded spindle  12  the jaws  10  move towards each other, while in the case of the counter-rotation of the threaded spindle  12  they move apart. The jaws  10 , their control of guidance and their adjustment means can be constructed in various known manner and as such do not comprise part of the invention. 
         [0019]    The jaws  10  respectively exhibit one hook receptacle  18 , in which hook module  20  can be seated. The hook receptacle  10  and the hook module  20  are so designed, that at least two hook modules  20  can be seated next to each other in the hook receptacle  18 . In the shown embodiment respectively five hook modules  20  are seated in a hook receptacle  18 . The hook receptacle  18  is provided on the jaws  10  in such a manner, that the hook modules  20  seated in the hook receptacle  18  are arranged side-by-side in a row, whereby this row runs perpendicular to the adjustment path of the jaws  10 , that is, in the illustrated embodiment according to  FIG. 1  transverse to the threaded spindle  12 . The hook module  20  carries hooks  22 . Each hook module  20  preferably carries only one hook  22 , however in certain cases the hook module  20  could exhibit several hooks  22 . The hooks  22  are stuck into the skin and form pull means anchorable in the skin at points. If these jaws  10  are advanced towards each other following the sticking in of the hooks into the skin, then thereby a pull force is introduced into the skin at points via the hooks  22 , as necessary for stimulation of tissue stretching. 
         [0020]    In the illustrated embodiments the hook receptacles  18  are in the form of hollow forms, preferably hollow quadratic shapes, in which the hook modules  20  can be inserted. The hook modules  20  exhibit a cross-section adapted to the quadric hollow shape of the hook receptacle  18 , so that in later described manner there are movable in the hook receptacle  18  perpendicular to the longitudinal axis of the profile, that is in the direction of the pull force or as the case may be in the movement direction of the jaws  10 . 
         [0021]    As can be seen particularly from  FIGS. 2 ,  3  and  5 , the hook modules  20  are divided into two groups in the hook receptacles  18 , whereby the hook modules  20  of the two groups in the hook receptacle  18  alternate. The hook module  20  of the one group, in the illustrative embodiment the hook modules  20 . 1 ,  20 . 3  and  20 . 5 , are thus set off by gaps with respect to the module  20  of the second group, in the illustrated embodiment the hook modules  20 . 2  and  20 . 4 . The hook modules  20 . 1 ,  20 . 3  and  20 . 5  and the hook modules  20 . 2  and  20 . 4  of the second group are respectively groupwise moveable relative to each other, as shown in  FIGS. 2 ,  3  and  5 . 
         [0022]    This opposing moveability of the hook modules  20  with the hooks  22  makes possible the following process for stretching the tissue of the skin. 
         [0023]    The hooks  22  are stuck into the skin to be stretched. For example, the hooks  22  of the two jaws  10  are stuck into the skin on the oppositely lying edges of a large surface area skin defect or a wound. The jaws  10  are then moved towards each other via the adjusting means  12 ,  14 , in order to bring the wound edges towards each other and to stretch the skin outside of the wound edges. In accordance with the invention the drive of the jaws  10  occurs in such a manner, that a high pull force is exercised on the skin via the hooks  22 . The pull force essentially may not exceed the tear resistance of the skin, which is approximately 15 N/mm 2  since in this case the hooks  22  would be torn from the skin. Since the hook module  20  of the one group is advanced in the pull direction, this high pull force is introduced into the skin essentially only via the hooks  22  of the advanced hook module, that is, in the representation according to  FIGS. 2 and 5 , by the hook modules  20 . 1 ,  20 . 3  and  20 . 5 , and in the representation according to  FIG. 3  by the hook modules  20 . 2  and  20 . 4 . The hooks  22  arranged side-by-side in the hook receptacle  18  exhibit a separation from each other of approximately 5-15 mm Thereby, the skin is tensioned and stretched by the group of advanced hook modules over the entire breadth of the hook receptacle  18 , while the retracted hook modules  20 . 2  and  20 . 4  lying between the advanced hook modules  20 . 1 ,  20 . 3  and  20 . 5  exercise upon the skin via their hooks  22  only a low pull force or even no pull force. 
         [0024]    The high pull force, which is introduced via the advanced hooks  22  of the hook module  20 . 1 ,  20 . 3  and  20 . 5  ( FIG. 2 ) in the skin has the consequence, that on the pressure side of the hooks  22  a compression pressure is exercised on the skin tissue, which exceeds the critical closure pressure of the venous capillary system of the skin tissue which lies at approximately 20-40 mm/Hg. This pull load of the tissue is thus maintained only for a period of time, which lies clearly below the ischemia tolerance of the skin tissue of approximately 7 hours. This time period lies between several minutes and several few hours. A shorter period of time of approximately minutes, for example less than 30 minutes, is possible in particular with an automatic controlled drive. A longer period of time of approximately 1-3 hours is preferred in the case of the employment of personnel for a manual adjustment. Following this time period the hook modules  20  of the two groups are displaced relative to each other, so that now the hook module  20  of the first group and the second group exchange their position. The hook modules  20 . 1 ,  20 . 3  and  20 . 5  of the first group move out of the position shown in  FIG. 2  towards the back and the hook modules  20 . 2  and  20 . 4  of the second group are then advanced towards the front so that the positions shown in  FIG. 3  are assumed. Now the high pull load, which is caused by the adjustment of the jaws  10 , is introduced into the skin by the hooks  22  of the second group. The hooks  22  of the retracted hook module  20  are relaxed and exercise upon the skin tissue lying on their pressure side little or no compression pressure. This compression pressure lies significantly below the critical closure pressure of the venous capillary system of the tissue, so that blood perfusion in the tissue on the pressure side of the hooks  22  occurs and a rapid restoration of blood flow through this tissue occurs. 
         [0025]    By the position exchange of the hook modules  20 . 1 ,  20 . 3  and  20 . 5  of the first group and the hook modules  20 . 2  and  20 . 4  of the second group occurring over set period of time it is possible to carry out the skin stretching over a long treatment duration of hours and days, wherein the maximal pull load can be exercised on the tissue continuously over the entire breadth of the hook receptacles  18 . The spot or point loading alternates thereby however in regular time intervals between the hooks  22  of the first group and the hooks  22  of the second group, so that despite the high pull load, a tissue damage due to low blood flow does not occur. 
         [0026]    The alternating displacement of the hook modules  20  of the first and second groups can be accomplished in various ways. 
         [0027]    In the embodiment according to  FIGS. 1 and 2  the hook modules  20  exhibit the shape of a cubic hollow body. An adjusting shaft  24  transitions through the hollow body of the hook module  20 , which exhibits on its one end an adjustment drive  26 . The adjustment drive is only shown schematically in  FIG. 2 . This adjustment drive  26  could be a rotation knob for a manual adjustment or an automatically controlled motorized drive for an automatic adjustment. On the adjustment shaft  24  are seated adjustment cams  28 , wherein for each hook module  20  an associated adjustment cam  28  is provided. The adjustment cams  28  are preferably in the form of so-called same-thickness and lie with their front and their rear profile inner surface against the hook module  20 . The adjustment cams  28  associated with the hook modules  20 . 1 ,  20 . 3  and  20 . 5  of the first group are displaced at an angle of  180 ° with respect to the adjustment cams  28  associated with the second group of hook modules  20 . 2  and  20 . 4 , as can be clearly seen from  FIGS. 1 and 2 . 
         [0028]    A rotation of the adjustment shafts  24  by 180° results in this embodiment in an exchange of the positions of the hook modules  20 . 1 ,  20 . 3  and  20 . 5  of the first group with the hook modules  20 . 2  and  20 . 4  of the second group. Since the adjustment cams  28  lie against the front and the rear inner wall surfaces of the hook modules  20 , the hook modules  20  are positively moved both in the forward movement as well as in the retraction movement by the adjustment cams  28 . The relaxation of the hooks  22  of the retracted hook module  20  occurs thus by force and independent of the elastic return spring force exercised by the skin upon these hooks. 
         [0029]    In  FIGS. 3 and 4  an alternative embodiment is shown. 
         [0030]    In this embodiment the adjustment shaft  24  runs behind the hook modules  20 . On the adjustment shaft  24  are seated adjustment cams  28 , which are respectively associated with the individual hook modules  20 . Therein the adjustment cams  28  which are associated with the hook modules  20 . 1 ,  20 . 3  and  20 . 5  of the first group are set off with respect to the adjustment cams  28  which are associated with the hook modules  20 . 2  and  20 . 4  of the second group by 90° on the adjustment shaft  24 , as can be seen in  FIG. 4 . In the representation according to  FIGS. 3 and 4  the adjustment cams  28  of the hook modules  20 . 2  and  20 . 4  are in engagement and push these hook modules in the advanced position. The adjustment cams  28  of the hook modules  20 . 1 ,  20 . 3  and  20 . 5  are in comparison thereto pivoted back, so that they release the associated hook modules. Upon a rotation of the adjustment shaft  24  by 90° (in  FIG. 4  in the counter-clock sense) the adjustment cams  28  of the other group come into engagement and push the associated hook modules  20 . 1 ,  20 . 3  and  20 . 5  in the active position while the adjustment cams  28  of the hook modules  20 . 2  and  20 . 4  are pivoted back and the associated hook modules are released. 
         [0031]    In this embodiment the hook modules  20  are positively moved in the advanced position and held there by the adjustment cams  28 . The inactive hook modules  20  are only released by the associated adjustment cams  28 , so that these are no longer supported. The hook module  20  moves back in this embodiment on the basis of the elastic return spring force of the skin acting upon the hooks  22 . The relaxed hook modules move back under the elasticity effect of the skin to the point that their hooks  22  no longer exercise any significant force on the skin. Thereby the compression force exercised by the relaxed hook modules  20  on the pressure side of the hooks  22  upon the skin tissue falls to practically zero. 
         [0032]    In  FIG. 5  a further embodiment is shown, in which the individual hook modules  20  are respectively associated with individual adjustment means  30 . These adjustment means can be of any construction, for example as adjustment screws or as shown in  FIG. 5  a pneumatic cylinder-piston adjustment means. Since the hook modules  20  are respectively individually adjustable via their associated adjustment means  30 , in this embodiment a flexible distribution of the pull forces over the breadth of the hook receptacles  18  is possible. In addition such an adjustment is suitable in particular for automation. If the adjustment means  30  additionally engage via an elastic pad or cushion  32  against the hook modules  20 , as indicated in  FIG. 5 , then the hook modules  20  can with their respective hooks  22  adapt to and equalize different skin tensions. 
         [0033]    In all embodiments of the invention the pull force acting to stretch the tissue is produced by the movement of the jaws  10 . This pull force is introduced constantly in the tissue, in particular also in the case of a long time stretching. The introduction of the pull force into the tissue is however over time periodically alternatingly distributed over various hooks. The hooks are thereby relaxed in regular time intervals, so that in the pressure areas the tissue perfusion is completely restored and no necrosis occurs. 
       REFERENCE NUMBER LIST 
       [0000]    
       
           10  Jaws 
           12  Threaded spindle 
           14  Drive 
           16  Threaded box 
           18  Hook receptacle 
           20  Hook module 
           22  Hooks 
           24  Adjustment shaft 
           26  Adjustment drive 
           28  Adjustment cam 
           20  Adjustment means 
           32  Pad