in fig1 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 fig1 . 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 . 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 fig1 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 . 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 . as can be seen particularly from fig2 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 fig2 and 5 . this opposing moveability of the hook modules 20 with the hooks 22 makes possible the following process for stretching the tissue of the skin . 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 fig2 and 5 , by the hook modules 20 . 1 , 20 . 3 and 20 . 5 , and in the representation according to fig3 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 . the high pull force , which is introduced via the advanced hooks 22 of the hook module 20 . 1 , 20 . 3 and 20 . 5 ( fig2 ) 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 fig2 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 fig3 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 . 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 . the alternating displacement of the hook modules 20 of the first and second groups can be accomplished in various ways . in the embodiment according to fig1 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 fig2 . 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 fig1 and 2 . 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 . in fig3 and 4 an alternative embodiment is shown . 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 fig4 . in the representation according to fig3 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 fig4 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 . 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 . in fig5 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 fig5 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 fig5 , then the hook modules 20 can with their respective hooks 22 adapt to and equalize different skin tensions . 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 .
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 .