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Paper text:
joint contracture tends to increase progressively in severity as the joint is kept immobile 
 for a prolonged period of time under the influence of joint fixation or illness .
one type of joint 
 contracture is acquired contracture , which develops after birth in the presence of some 
 factors .
depending on the factors responsible , acquired joint contracture has been 
 subdivided into cutaneous contracture , connective tissue contracture , myogenic contracture , 
 neurogenic contracture , and arthrogenic contracture ( contracture of joint origin)1 . of these types of joint contractures , 

cutaneous contracture is usually considered to develop from skin burns , injury , scarring , 
 etc2 .
stretching of the affected skin in 
 cases of burns has been used as a means of treating scar contracture .
this therapy has been 
 shown to be effective at improving the extensibility of scarred tissue3 and expanding the area of the scarred tissue4 .
these previous reports indicate the 
 efficacy of skin stretching on cutaneous contracture arising from scarring .
it has also been shown that the skin is involved in disuse joint contracture arising from 
 joint fixation or immobility5,6,7 .
our previous study 
 demonstrated that 2 weeks of joint fixation reduced the extensibility of the overlying 
 skin8 .
joint movements are normally 
 accompanied by stretching of tissues such as the skin and muscles ; however , even in cases 
 when a joint is impossible to move , the skin retains its capability to stretch without 
 moving the joint . maintaining the extensibility of the skin
may potentially minimize the 
 progression of joint contractures , even when the joints can not be moved .
however , no 
 previous study has elucidated whether skin extensibility can be maintained by stretching the 
 skin without performing any joint movement .
the present study was designed to examine the possibility of maintaining the skin 
 extensibility through stretching of the involved skin in cases of disuse joint 
 contracture .
the animals used in this experiment were 8-week - old female wistar rats ( n=18 ) .
the animals 
 were housed in cages and given free access to food and water .
the environment of the animal 
 care room was maintained at a constant room temperature of 23  c with an air conditioner , 
 and day and night were artificially regulated by setting lights - on for 12  h and lights - off 
 for 12  h each day .
this animal experiment was conducted in accordance with the national 
 institute of health ( nih ) guide for the care and use of laboratory animals , and the 
 experiment was carried out with the approval of the research ethics committee of the 
 prefectural university of hiroshima .
six rats were allocated to the control group , 
 which received no intervention for the right ankle joint .
another 6 rats were allocated to 
 the fixation group , in which the right ankle joint was fixed in maximum plantar - flexion with 
 a cast for one week .
the remaining 6 rats were allocated to the stretching group , which 
 received fixation of the right ankle joint in maximum plantar - flexion with a cast , and 
 stretching of the dorsal skin over the ankle joint once daily for 30 minutes with the cast 
 removed during the skin stretching , which was performed without joint movement .
pentobarbital 
 ( 40  mg / kg ) was injected intraperitoneally ( i.p . ) , and under anesthesia the ankle joint was 
 held in full plantar flexion and immobilized with a plaster cast from the thigh to the foot 
 area9 . in order to prevent the cast from 
 breaking or falling off , it was covered with a stainless steel net . during the fixation 
 period , close attention was paid to the onset of edema and cast loosening , and the cast was 
 renewed as needed . in the stretching group , skin stretching was performed after removal of 
 the net and the cast , under anesthesia induced by intraperitoneal injection of pentobarbital 
 sodium ( 40  mg / kg , i.p . ) . during the stretching ,
the rats were placed in the lateral 
 decubitus position , with the right ankle joint placed upwards and kept in maximum 
 plantar - flexion to avoid ankle joint movement .
stretching was carried out using an 
 unstretchable segment of tape which could be attached to the skin , so that only the skin 
 could be stretched , without any motion of the joint .
one tape was attached to each of the 
 proximal and distal parts of the rat s right achilles tendon . the skin was stretched along 
 the major axis of the leg in both the proximal and distal directions .
a stretching force 
 equal to 0.3 n was applied with the use of a spring scale , following the method of a 
 previous study10 .
skin extensibility was evaluated using a tensile strength testing machine ( autograph 
 tensile tester model ag-50kng , shimadzu corporation ) on the last day of the experiment8 .
the skin sample for the test was obtained 
 from over the achilles tendon . during maximum plantar - flexion of the ankle joint ,
the skin 
 was marked at 2 points : point a , 3  mm distal to the heel ; point b , 10  mm proximal to point 
 a. the length of the skin sample between the distal end ( 5  mm distal to point a ) and the 
 proximal end ( 5  mm proximal to point b ) was 20  mm and its width was 4  mm .
holes were made at points a and b of 
 the skin sample , and an unstretchable stainless steel wire was inserted through the holes , 
 followed by fixation of both ends of the wire on the tensile testing machine with the use of 
 a clamp .
the test start point of the sample was adjusted with calipers , so that the distance 
 between the two points of wire insertion was 10  mm ( the distance between the two marked 
 points ) .
the tensile strength test was conducted once on each skin sample , with the starting 
 distance of the stretch set at 0  mm and the starting tension at 0 n. the extent to which the 
 skin was stretched by the force of 0.3 n from the start point was measured as an indicator 
 of the skin extensibility .
the non - parametric 
 kruskal - wallis test was used to compare skin extensibility .
a significant difference was concluded to exist at a probability 
 value of less than 5% in all of the statistical tests .
the results of the skin extensibility test are shown in table 1table 1.the changes in skin extensibilitygroupdistension distance ( mm)control5.1  0.7fixation2.8  0.4 * stretching3.7  0.4 * values are mean  sd . *
significant decrease compared to the control group ( p<0.05 ) 
 significant increase compared to the fixation group ( p<0.05 ) .
statistical analysis of the data revealed significant differences in the skin 
 extensibility among the three groups .
the skin extensibility was significantly lower in the 
 fixation and stretching groups than in the control group .
significant decrease compared to the control group ( p<0.05 ) 
 significant increase compared to the fixation group ( p<0.05 )
this study examined whether or not skin stretching , without any joint motion , would allow 
 skin extensibility to be maintained . stretching is usually performed to cause the soft 
 tissues to be stretched while moving the joint .
the effects of stretching have been 
 evaluated in previous experimental studies11 , 12 . in previous experiments using animals , 

the ankle joints of rats were fixed in maximum plantar - flexion with the use of a cast and 
 the range of motion of the ankle joint was measured after repetition of once daily 
 stretching of the plantar muscles originating in the ankle joint with the cast removed 
 during stretching . in these experiments ,
continuous stretching ( 30  min / day ) resulted in 
 suppression of the onset of joint contracture13 . in human experiments measurement of the passive torque after 
 repeated stretching of the ankle joint in the direction of dorsiflexion ( 30  min / sess ) showed 
 there was a decrease in the passive torque in this direction14 . in these past experiments , the efficacy of stretching
while the 
 joint was moved was manifested by improvement of the muscle extensibility , and the target of 
 the stretching was the muscles .
however , it has been reported that the tissues responsible 
 for joint contracture are not confined to skeletal muscles , but include the skin as 
 well5,6,7 .
as is the case with skeletal muscle , the 
 skin can also be stretched by the motion of stretching while moving the joint . in cases 

where the joint is forced to be fixed with a cast , stretching of the skin without the joint 
 moving at the same time is possible if a window is opened in a part of the cast .
therefore , unlike in previous 
 studies , it was determined that in this study , the effects of stretching exercises targeting 
 exclusively the skin would need to be examined by carrying out those exercises without joint 
 movements to prevent them from exerting effects on the muscles .
the results of the present study indicate that skin stretching without joint motion can 
 also maintain skin extensibility .
tissue expansion was previously reported as a method of 
 stretching the skin without moving the joint . in the technique of tissue expansion
, a 
 capsule is inserted under the skin and gradually inflated to cause stretching of the skin 
 and soft tissues15 .
used a 
 tissue expander in male patients with scarring alopecia caused the skin of the hair - covered 
 scalp to stretch and replace the skin of the area of hair loss16 .
used a tissue expander in patients with 
 nevus to stretch the skin of the inguinal and hypogastric regions , followed by use of the 
 stretched skin to cover the nevus - affected area17 .
the results of these studies indicate that tissue expansion can 
 improve skin elasticity through stretching of the skin .
however , because tissue expansion 
 involves surgical stress , it is never used to suppress the onset of disuse joint 
 contracture .
the present study is significant in that it revealed the efficacy of skin 
 stretching on the body surface without movement of the joint .
the reported changes in skin area stretched 
 by the tissue expansion technique include epidermal cell proliferation18 , epidermal thickening19 , dermal thinning20 , etc .
the improvement in the skin extensibility observed in the 
 present study , following stretching without simultaneous joint movement , seems to be 
 explained by changes in the skin similar to those reported by previous studies .
however , 
 although morphological changes and biochemical changes should have been examined , these were 
 beyond the scope of our study . as a result
morphological and biochemical changes in the skin will need to be investigated 
 after performing stretching exercises without joint movements .
[ purpose ] this study examined the possibility of maintaining skin extensibility by 
 stretching the skin involved in disuse joint contracture . [ subjects and methods ] the study 
 was carried out using 18 male wistar rats . 
 the rats were randomly allocated to three 
 groups . 
 the control group received no intervention for the right ankle joint , the fixation 
 group received one - week s fixation of the right ankle joint in maximum plantar - flexion 
 with a cast , and the stretching group received continuous stretching of the skin over the 
 achilles tendon for 30  min once daily for one week with the cast removed during the skin 
 stretching , but the joint was not moved . on the final day , skin extensibility of the skin 
 from the posterior aspect of the ankle joint was determined using a tensile strength 
 tester and a length - tension curve . 
 [ results ] statistical analysis of the data revealed 
 significant differences in the skin extensibility among the three groups . 
 the stretching 
 group showed significantly greater improvement of skin extensibility than the fixation 
 group . [ conclusion ] skin stretching without moving the joint 
 was demonstrated to be useful 
 for maintaining skin extensibility .